Process to prepare propylene

1. A process for preparing propylene from a hydrocarbon feedstock fraction comprising between 5 and 50 wt % olefin hydrocarbon compounds having 4 or more carbon atoms, the process comprising:

isolating the hydrocarbon feedstock from an effluent of a fluid catalytic cracking process;

contacting the hydrocarbon feedstock fraction with a mixture of a heterogeneous cracking catalyst and a heterogeneous dehydrogenation catalyst obtain propylene and other reaction products;

wherein the heterogeneous cracking catalyst and the heterogeneous dehydrogenation catalyst are present as separate particles in one or more packed beds in an in-series configuration, each packed bed comprising the heterogeneous cracking catalyst and the heterogeneous dehydrogenation catalyst;

wherein the hydrocarbon feedstock fraction, the propylene, and the other reaction products flow from an up-flow region to a down-flow region following a flow path;

wherein in the direction of the flow path a concentration of the heterogeneous dehydrogenation catalyst in the one or more packed beds gradually or step-wise increases compared to the heterogeneous cracking catalyst; and

wherein a content in the volume percent of the heterogeneous dehydrogenation catalyst particles relative to the total volume of catalyst particles varies from between 0% to 50% at a start of the flow path to between 20% and 100% at an end of the flow path.

2. The process according to claim 1 , wherein the hydrocarbon feedstock is contacted with the mixture of the heterogeneous cracking catalyst and the heterogeneous dehydrogenation catalyst at process conditions including a temperature of between 300 and 750° C., an absolute pressure of between 0.1 and 10 MPa and a weight hourly space velocity (WHSV) of higher than and including 50/hour.

3. The process according to claim 2 , wherein the hydrocarbon feedstock fraction is contacting with the mixture of the heterogeneous cracking catalyst and the heterogeneous dehydrogenation catalyst in the presence of dilution steam.

4. The process according to claim 2 , wherein the temperature is between 450 and 600° C., wherein the absolute pressure is between 0.1 and 0.5 MPa and wherein the weight hourly space velocity (WHSV) is higher than 100/hour.

5. The process according to claim 1 , wherein the heterogeneous cracking catalyst comprises an acidic material.

6. The process according to claim 5 , wherein the acidic material is a molecular sieve or an amorphous or semi-crystalline material chosen from the group of alumina, boehmite alumina, gamma alumina, theta alumina, silica alumina, silica-titania, silica-tungsten, silica phosphorous, and silica-alumina-phosphorous.

7. The process according to claim 6 , wherein the molecular sieve is selected from the structure types consisting of: BEA, CHA, MOR, MFI, MEL, IMF and TUN.

8. The process according to claim 1 , wherein the heterogeneous cracking catalyst:

(a) further comprises a carrier which does not have strong acidic sites, or

(b) does not comprise a molecular sieve and does comprise a material having strong acid sites.

9. The process according to claim 1 , wherein the heterogeneous dehydrogenation catalyst comprises any one or more of:

(a) a transition metal or a noble metal, one or more additive components and a carrier;

(b) an oxydehydrogenation catalyst; and

(c) a separate solid oxygen source catalyst particle.

10. The process according to claim 9 , wherein the transition metal is Cr or the noble metal is Pt.

11. The process according to claim 9 , wherein the oxydehydrogenation catalyst or the separate solid oxygen source catalyst particle, or both, comprises a reducible metal oxide of at least a transition metal.

12. The process according to claim 1 , wherein the heterogeneous cracking catalyst and the heterogeneous dehydrogenation catalyst are

present in one packed bed.

13. The process according to claim 1 , wherein propylene is isolated from an effluent as discharged from the one or more packed or beds from higher boiling compounds, and wherein all or part of the higher boiling compounds are recycled to the one or more packed beds.

14. The process according to claim 13 , wherein in the all or part of the higher boiling compounds are recycled to an intermediate position along the flow path.

15. The process according to claim 1 , wherein the hydrocarbon feedstock fraction which is contacted with the mixture of the heterogeneous cracking catalyst and the heterogeneous dehydrogenation catalyst in the one or more packed beds has been subjected to an aromatics extraction step and wherein the hydrocarbon feedstock fraction has an aromatics content of less than 20 wt %.